1. Field of the Invention
The present invention relates to improvement of handheld type four-cycle engines which can desirably be used mainly as a power source for machines for portable operation such as trimmers.
2. Description of the Relevant Art
With regard to conventional handheld type four-cycle engines, one in which an oil mist generated from the oil stored in an oil reservoir is circulated inside the engine in order to lubricate the inside of the engine regardless of the operational position of the engine is already known in Japanese Patent Application Laid-open No. 10-288019.
However, the lubrication system disclosed in the above-mentioned patent publication has a comparatively long and complicated circulation route in which the oil mist is circulated from the oil tank to the crank chamber, then to the valve operation chamber and is then returned to the oil tank. Such a long and complicated circulation route for the oil mist causes an increase in the size of the engine main body, which includes the circulation route, and makes it difficult to reduce the weight thereof. Weight reduction is one of the important issues when considering improvements in the operability of, in particular, handheld type four-cycle engines.
The present invention has been carried out in view of the above-mentioned circumstances, and it is an object of the present invention to provide a handheld type four-cycle engine which can reliably lubricate the valve operation mechanism regardless of the operational position of the engine while making the engine main body more compact and lighter.
In accordance with a first characteristic of the present invention in order to achieve the above-mentioned objective, there is proposed a handheld type four-cycle engine including a crankcase having a crank chamber housing a crankshaft; a cylinder block having a cylinder bore; and an intake valve, an exhaust valve and a valve operation mechanism provided in a side wall of the cylinder block, the valve operation mechanism being operable in association with the crankshaft so as to open and close the intake valve and the exhaust valve, wherein an oil tank for storing oil is provided in one side wall running the length of the crankcase and the cylinder block, and the oil tank houses the valve operation mechanism and oil mist generation means for generating oil mist from the stored oil.
In accordance with the above-mentioned first characteristic, since the oil tank can be filled with the oil mist generated by the oil mist generation means, each part of the valve operation mechanism disposed inside the oil tank can be lubricated reliably by the above-mentioned oil mist regardless of the operational position of the engine. It is therefore unnecessary to provide the engine main body with a special oil supply passage for lubricating the valve operation mechanism, and the size and weight of the engine can thus be reduced. Moreover, since the oil tank is provided in one side wall running the length of the crankcase and the cylinder block, it is unnecessary to provide an oil reservoir in the lower part of the crankcase, and the total height of the engine can thus be reduced and the size of the engine can be further reduced.
In accordance with a second characteristic of the present invention, in addition to the above-mentioned first characteristic, there is proposed a handheld type four-cycle engine wherein an outward route and an return route are provided for communication between the oil tank and the crank chamber above the oil stored in the oil tank, and valve means is provided for introducing the positive pressure component of pressure pulsations generated in the crank chamber into the side of the oil tank.
The above-mentioned valve means corresponds to the one-way valve 51 described in the embodiment of the present invention below.
In accordance with the above-mentioned second characteristic, since the oil mist generated in the oil tank is circulated between the oil tank and the crank chamber by utilising the pressure pulsations of the crank chamber, the crankshaft and the piston can be lubricated regardless of the operational position of the engine. Moreover, since it is sufficient for the oil mist to merely circulate between the two chambers, that is to say, the oil tank and the crank chamber, the outward and return routes for providing communication between the two chambers can be made comparatively short and simple, and the size and weight of the engine can be further reduced.
In accordance with a third characteristic of the present invention, in addition to the above-mentioned first or second characteristics, there is proposed a handheld type four-cycle engine wherein a breather chamber is communicated with the return route between the valve means and the oil tank, and the breather chamber is communicated with an air cleaner of an intake system on one side and with a suction chamber communicated with the oil tank via an orifice on the other side.
In accordance with the above-mentioned third characteristic, the blowby gas generated in the crank chamber is transferred to the breather chamber together with the oil mist, and separated into gas and liquid. Then, the blowby gas is discharged to the air cleaner, and the liquefied oil flows into the suction chamber via the orifice and can be returned to the low pressure oil tank.
Furthermore, in accordance with a fourth characteristic of the present invention, there is proposed a handheld type four-cycle engine including a crankcase having a crank chamber housing a crankshaft; a cylinder block having a cylinder bore; and an intake valve, an exhaust valve and a valve operation mechanism provided in a side wall of the cylinder block, the valve operation mechanism being operable in association with the crankshaft so as to open and close the intake valve and the exhaust valve, characterised in that an oil tank for storing oil that is separate from the crank chamber is provided in one side wall running the length of the crankcase and the cylinder block, the oil tank houses the valve operation mechanism and oil mist generation means for generating oil mist from the stored oil and is arranged so that the oil mist generated inside the oil tank can be supplied to the crank chamber, a cooling fan driven by the crankshaft is placed so as to adjoin the oil tank, and a power output mechanism is provided on the crankshaft so that the crankcase is interposed between the power output mechanism and the oil tank.
In accordance with the above-mentioned fourth characteristic, since the oil tank is provided in one side wall running the length of the crankcase and the cylinder block, it is unnecessary to provide an oil reservoir in the lower part of the crankcase, the total height of the engine can thus be reduced and the engine can be made compact. Moreover, since the oil tank is filled with the oil mist generated by the oil mist generation means and the oil mist is supplied to the crank chamber, each component inside the crank chamber as well as the valve operation mechanism placed inside the oil tank can be lubricated reliably regardless of the operational position of the engine.
Furthermore, since the cooling fan is placed so as to adjoin the oil tank, the oil tank and, therefore, the stored oil and the oil mist inside the oil tank can be cooled effectively by the cooling air generated by the cooling fan, thus efficiently carrying out lubrication and cooling of each component.
Moreover, since the valve operation mechanism and the power output mechanism are linked to the two ends of the crankshaft, the loads arising from the valve operation mechanism and the power output mechanism, during operation of the engine, are applied to the two separate ends of the crankshaft, it is thus possible to prevent the load applied to the crankshaft, its bearings and the side wall of the crankcase from being localised and the durability thereof can be enhanced.
In accordance with a fifth characteristic of the present invention, in addition to the above-mentioned first or fourth characteristic, there is proposed a handheld type four-cycle engine wherein a carburettor and an exhaust muffler are placed on the two sides of the cylinder block along a direction perpendicular to the axes of both the cylinder bore and the crankshaft.
In accordance with the above-mentioned fifth characteristic, the carburettor and the exhaust muffler can be easily arranged without any obstruction from the oil tank, the cooling fan or the power output mechanism thus helping to make the engine more compact.
The above-mentioned oil mist generation means corresponds to the oil slingers 36 to 41 described in the embodiment of the present invention below, and the above-mentioned power output mechanism corresponds to the centrifugal clutch 31 described in the embodiment below.
The above-mentioned objectives, other objectives, characteristics and advantages of the present invention will become apparent from an explanation of preferable embodiments which will be described in detail below by reference to the attached drawings.